1. Field of the Invention
The present invention relates to a display device, and more particularly, to a terminal portion for inputting a signal from outside.
2. Description of the Related Art
In a liquid crystal display device, on a surface of one substrate of a pair of substrates arranged so as to be opposed to each other while sandwiching liquid crystal, the surface being on the liquid crystal side, there are formed gate lines (scanning signal lines) extending in an X direction and arranged in parallel to one another in a Y direction, and drain lines (video signal lines) extending in the Y direction and arranged in parallel to one another in the X direction. Rectangular regions surrounded by the respective signal lines are formed as pixel regions. A display region is formed of a mass of those respective pixels. Each of the pixels includes at least a thin film transistor which is turned ON in response to a scanning signal from the gate line, and a pixel electrode to be supplied with a video signal from the drain line via the thin film transistor in the ON state. Those gate line and drain line are each connected to one end of terminal wiring (extraction wiring) at an end portion of the display region, and are each electrically connected to a terminal called a pad formed at another end of the terminal wiring. The terminal wiring is arranged in a periphery region excluding the display region, and the terminals are arranged at a side portion of the one substrate.
In each of those terminals, for example, as described in Japanese Patent Application Laid-open No. 2004-333673, an opening portion having a width smaller than that of the terminal wiring is formed in a part of an insulating film arranged on the terminal wiring, and a conductive layer corresponding to the opening portion is formed. Thus, the conductive layer and the terminal wiring are electrically connected to each other. In this case, in a region in which the conductive layer is to be arranged, there are formed two grooves (elongated holes), from which an insulating film provided below is exposed, at side portions of the terminal wiring along an extension direction of the terminal wiring. The conductive layer is formed only on a region of the terminal wiring sandwiched between the two elongated holes, and the insulating film is formed on the terminal wiring arranged on both sides of the elongated holes.
In the terminal portion having such a structure, the terminal is connected to the drain line via the terminal wiring, and the drain line is connected to a drain electrode of each thin film transistor. Meanwhile, the terminal wiring extended from the terminal toward another end is electrically connected to a wiring layer CL arranged in the vicinity of a side edge portion of the substrate. Similarly, the respective terminals are connected to the same wiring layer CL, and thus all the terminals are short-circuited. The wiring layer CL is cut off when the glass substrate is cut. With this, the respective terminals are not short-circuited, that is, the terminals are electrically separated from one another.
Meanwhile, there is known a display device in which, on apart of a region outside the display region, a lighting inspection circuit for inspecting disconnection of the gate line or the drain line and the like is formed. For example, the lighting inspection circuit includes an inspection thin film transistor formed at end portions of the gate line and the drain line, which are not connected to the terminal wiring, an inspection signal line for turning ON the inspection thin film transistor, and an inspection signal line for supplying an inspection signal to the gate line or the drain line via the inspection thin film transistor in the ON state. Those inspection signal lines are also arranged in the periphery region excluding the display region together with the terminal wiring, and a terminal for inputting the inspection signal is also arranged in the side portion of the one substrate together with the terminal of the terminal wiring.
In the inspection of the liquid crystal display panel with use of this lighting inspection circuit, the inspection signal is input from the inspection terminal after the liquid crystal display panel is cut, thereby inspecting lighting and extinction of respective pixels aligned in matrix inside the display region.
That is, the inspection terminal is used only when the inspection signal is input from outside, and after the inspection is finished, only the inspection signal lines are used. That is, the conventional liquid crystal display panel includes wiring which is used as the terminal wiring during ordinary use after the inspection is finished and is used as the inspection signal lines during inspection. Only in this inspection wiring, the terminal portion is formed in the middle of the wiring, and during ordinary use, the terminal portion is not used.
However, as described above, the upper layer of the terminal portion is formed only of a conductive layer so as to input the inspection signal from the outside, and is not covered with an insulating film similarly to other signal line portions. Further, unlike terminal portions of other terminal wiring, a drive circuit, a flexible printed circuit board, and the like are not connected to the terminal portion. Therefore, when the liquid crystal display panel is used in, for example, a high-temperature and high-humidity environment, a portion exposed from the insulating film, such as the conductive layer formed on the terminal wiring, is subjected to corrosion due to a mutual action of moisture in the air and an electric field applied to the conductive layer. Due to the progress of this corrosion, the terminal wiring formed under the conductive layer may also be affected, and hence there is a fear that the terminal wiring is disconnected.